Data transfer using optical frequency carrier waves generated by sources such as lasers or light-emitting diodes is becoming increasingly important. One means for conducting or guiding such optical frequency carrier waves from one point to another is an optical waveguide. Optical waveguides encompass a first medium which is essentially transparent to the light of the optical frequency carrier waves and a second medium having a lower refractive index than that of the first medium. The first medium is surrounded by, or otherwise enclosed within, the second medium. Light introduced into an end of the first medium undergoes total internal reflection at the boundary with the second medium and thus is guided along an axis of the first medium. Perhaps the most frequently used optical transport medium is glass formed into an elongated fiber.
However, while glass optical fibers are convenient for data transfer over long distances, they are inconvenient for complex high-density circuitry because the high density of such circuitry makes their use problematic and expensive. Polymeric materials, on the other hand, hold great promise for constructing cost effective, reliable, passive and active integrated components capable of performing the required functions for integrated optics.
Therefore, considerable effort has been directed to forming optical coupling devices and more recently to optical waveguides that can be formed of polymeric materials using photohardenable techniques. For example, in U.S. Pat. No. 5,292,620, to Booth et al., waveguide structures having a predetermined geometry and a process for forming these structures using photohardenable techniques are disclosed. The structures of the '620 patent encompass at least one buried channel waveguide in a laminated matrix where the waveguide and any connecting structures are first formed in a photohardenable film detachably disposed on a supporting substrate. After such first forming, the photohardenable film is detached from the supporting substrate and laminated between first and second photohardenable layers. In this manner, regions of the photohardenable layer adjacent the waveguide channel region and any connecting structures serve as cladding regions in the plane of the layer and the first and second photohardenable layers serve as cladding layers above and below that plane.
On the other hand, JP laid-open patent publications Nos. 2004-35838 H10-48443 and 2001-296438 disclose a method of exposing a polymer film to an actinic radiation, to change the chemical structure of the polymer so as to obtain a waveguide structure.